This invention relates to a tool for use in carrying out a cutting process, and more particularly to a cutting tool formed so that it can be used to cut an iron material of a high hardness and thereby obtain a mirror-polished surface thereon.
A cutting tool having an edge consisting of monocrystalline diamond is known well, which is used as a tool for precision cutting or mirror polishing a material of a non-ferrous metal, such as aluminum and copper.
When an iron material, for example, hardened carbon steel and stainless steel is cut with such a cutting tool using diamond, the diamond reacts with the iron due to the cutting heat to produce carbide, so that the diamond wears rapidly. This hampers a normal cutting operation.
Therefore, a cutting tool in which an edge is formed on a crystal which is obtained by sintering crystals of boron nitride is used to cut an iron material. This cutting tool is formed by, for example, attaching a tip formed of a polycrystalline sinter to a shank via a base. A chamfer and a relief surface are formed on an edge of the tip. Even if the relief surface, which has influence upon the roughness of a cut surface, of such a cutting tool is formed by cutting the mentioned material and polishing the same so that the roughness of surface becomes not more than 0.05 .mu.m Rmax, a mirror surface having a roughness of surface exceeding 0.1 .mu.m Rmax cannot be obtained.
The cause of this inconvenience resides in that the sharpness of a relief surface, which constitutes a blade, and an edge, which is formed of a face, in a tip consisting of polycrystalline sinter cannot be secured due to the micro-chipping of a binder with which the crystal grains are bound.
According to the specification of Japanese Utility Model Application No. 62592/1982 (Japanese Utility Model Laid-Open No. 164603/1983), a tip for a precision processing tool is proposed, in which grains of monocrystal of cubic boron nitride are used at an edge of the blade thereof. If different surfaces of a monocrystal and different orientations thereof are used as the relief surface of a blade and cutting direction, respectively, the abrasion characteristics of the tool differ greatly. No consideration is given to this matter in the tool proposed by the above utility model application.